No you can't round to 5mm or 10mm, it is millimeters, centimeters or meters and then you can set the decimal precision.
As other have said try not to adjust dimensions - show it for what it really is.
If it ends up something and 12mm from a site boundary then so be it.
At least you are being as accurate as you can be.
The tradie will round it up or down to the nearest 5mm or 10mm no doubt.
One of the forum moderators.
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